The present invention relates to a vertical MOSFET which takes measures for preventing device puncture due to breakdown.
MOS structures, whose major current flow was perpendicular to the surface of the structure, have been employed mainly in the fabrication of MOS power transistor devices. Because the relative lightly doped channel is quite short between the source and drain regions of the MOS power transistor devices, substantial bipolar transistor action can be induced. In application for a switching element, the MOS transistor is possibly applied with high voltage surge during switching, incurring breakdown current which tends to be concentrated to a certain portion of the parasitic transistor and which renders the transistor to be broken.